Tuesday, February 16, 2016

When global warming isn't global

Warmists have cottoned on to the fact that their feared 2 degree temperature rise doesn't sound very fearsome to most people. Most of us experience a temperature range of around 10 degrees in any 24 hour period -- sometimes a lot more. So Warmists now want to say that 2 degrees is only an average and that some places on earth will experience a temperature rise of much more than 2 degrees even if the average is 2 degrees. That is reasonable enough. It's basic statistics. An average implies a range.

Note firstly, however, that their study is of climate EXTREMES only, not of averages. The two are presumably related but to what degree is not pursued. Let's be charitable, however, and assume that what they tell us applies to averages too.

They seem rather lost, however, to explain just why some regions will be hotter. The best they can do is to note that the oceans warm more slowly so an average which includes the oceans will imply land temperatures that are hotter than 2 degrees.

And from that they trot out climate models that purport to study large regions of the earth separately. And they find, for instance, "a 2.2°C warming of extremes around the Mediterranean basin". That doesn't sound too scary, however. So they add: "At 1.5°C we would still see temperature extremes in the Arctic rise by 4.4°C". But how scary is that? Arctic temperatures are way below the freezing point of water so even a 4.4 degree rise would not melt anything. And most Arctic ice is sea ice anyway so melting that would have no effect on the sea level -- as Archimedes showed around 3,000 years ago

But it's all based on modelling and the authors themselves supply in their paper a long list of reasons why it could all be wrong. So their general point is reasonable but any specific temperature projection has to be taken with a large grain of salt

Given their alarmist aims, the projections should in fact probably be taken as maxima. So, in that light, they are rather reassuring about the regional effects of any future global warming

Popular article below followed by the journal abstract

Regions around the Arctic may have passed a 2°C temperature rise as far back as 2000 and, if emissions rates don't change, areas around the Mediterranean, central Brazil and the contiguous United States could see 2°C of warming by 2030.

This is despite the fact that under a business as usual scenario the world is not expected to see global average temperatures rise by 2°C compared to preindustrial times until the 2040s.

New research published in Nature led by Prof Sonia Seneviratne from ETH Zurich with researchers from Australia's ARC Centre of Excellence for Climate System Science (ARCCSS) has quantified the change in regional extremes in a world where global average temperatures have risen by 2°C.

The research shows worldwide warming extremes over land generally exceed the rise in this scenario, in some cases by as much as 6°C. "We even see starkly different rates of extreme warming over land even when global average temperatures reach just 1.5°C, which is the limit to the rate of warming agreed to at the Paris talks," said lead author Prof Seneviratne.

"At 1.5°C we would still see temperature extremes in the Arctic rise by 4.4°C and a 2.2°C warming of extremes around the Mediterranean basin."

The extreme regional warming projected for Alaska, Canada, Northern Europe, Russia and Greenland could have global impacts, accelerating the pace of sea-level rise and increasing the likelihood of methane releases prompted by the melting of ice and permafrost regions.

"The temperature difference between global average temperatures and regional temperature extremes over land not only has direct climate impacts, it also means we may have to reconsider the amount of carbon dioxide we can emit," said co-author and Director of ARCCSS Prof Andy Pitman.

"For instance, to keep extreme temperature changes over the Mediterranean below a 2°C threshold, the cumulative emissions of CO2 would have to be restricted to 600 gigatonnes rather than the 850 gigatonnes currently estimated to keep global average temperatures increase below 2°C."

According to the researchers, if global average temperatures warm by 2°C compared to preindustrial times this would equate to a 3°C warming of hot extremes in the Mediterranean region and between 5.5 -- 8°C warming for cold extremes over land around the Arctic. Most land-masses around the world will see an extreme temperature rise greater than 2°C.

One of the few exceptions is Australia -- famously known as a land of droughts and flooding rains. The projections show little difference between global average temperatures and a change in its extreme regional temperatures.

"This might be something peculiar about Australia's climate, or perhaps it highlights problems with the climate models," said Prof Pitman.

"If the latter, there is a risk Australia will lack warnings about the increases in extremes that are now clearly available to Northern Hemisphere countries."

He said this potential hole in understanding of climate extremes climate needs urgent resolution with more focused model development in the southern hemisphere.

The researchers also note the paper did not take into account unexpected changes in the climate system.

"What this research cannot take into account are abrupt climate shifts known colloquially as "tipping points"," said ARCCSS co-author Dr Markus Donat.

"We have no way of knowing when our climate may change abruptly from one state to another meaning we could potentially see even greater regional variation than these findings show."

Allowable CO2 emissions based on regional and impact-related climate targets

Sonia I. Seneviratne et al.

Abstract

Global temperature targets, such as the widely accepted limit of an increase above pre-industrial temperatures of two degrees Celsius, may fail to communicate the urgency of reducing carbon dioxide (CO2) emissions. The translation of CO2 emissions into regional- and impact-related climate targets could be more powerful because such targets are more directly aligned with individual national interests. We illustrate this approach using regional changes in extreme temperatures and precipitation. These scale robustly with global temperature across scenarios, and thus with cumulative CO2 emissions. This is particularly relevant for changes in regional extreme temperatures on land, which are much greater than changes in the associated global mean.